Transmission FUBAR

[Marcmedic]

OK. H2 ran fine yesterday. Today, the damn thing won't shift right. I only have 2nd and 3rd gear. After driving and the truck and it shifts to 3rd gear, it won't downshift after coming to a complete stop. Downshifting manually into first only downshifts the truck to 2nd gear. So essentially I only have 2nd and 3rd gear and have to manually downshift every time. This ever happened to anyone else? Of course this happens when I'm on a 72 hour shift and don't get off until Saturday morning. Trans fluid level is fine. Any ideas?